Intrusion of minute metallic particles, in particular copper, into the vitreous body of the eye, upon injury leads in many cases to blindness, through damage caused to the retina by ions of these metals (metallosis). A method is attempted to determine the nature of the metallic particle in vivo and the changes in ion concentration with time. The eye will be irradiated by monochromatic X-rays (employing and X-ray tube and monochromator) and the resulting X-ray fluorescence of the metal ions (if present) will be measured by means of a Si (Li drifted) solid state counter in conjunction with a multichannel analyzer.